carburetor or spark plugs
A 1.9 TDI can hum at idle if the spark plugs foul. A clogged fuel filter can also cause this issue.
1978 80 Mercury Outboard IDLE ADJUSTMENT
You adjust idle with idle timing
outboard motor will start and idle, but dies out under load
It's my guess, and only a guess, that the idle jet is either plugged or the idle screw is turned in too tight. Judiously apply some carb cleaner and open the screw 3/4 of a turn. Once you get it running, play with the screw to smooth it out.
The Dodge ram 1500 rough idle can because by a bad spark plug or spark plug wire. The rough idle can also because by a bad camshaft.
== Is this engine the plastic cowling with idle knob and choke knob on the front pull it to choke and turn to raise idle? = Read more: http://www.justanswer.com/questions/1dpbt-25-hp-mercury-outboard-water#ixzz0HH1RenQM&B
With mine, the rough idle was fixed by changing the spark plug wires.
Maybe it's running too rich.check the gear oil to see if it's clear or discolour.if it's discolour the seals in the gear section of the engine is bad and the gear oil will enter the piston chamber and it will foul the spark plug. this will kill the engine when you come to a idle or you're not using the correct spark plug
Bad spark plugs can indeed cause an engine to idle rough. If any of the spark plugs are misfiring or are not producing enough of a spark to ignite the fuel, then not only will the engine idle roughly, it will alwso waste gas. If may seem as though it is running fine when you are driving however, you still may be wasting gas and your pickup may not be as fast as it should.
A fouled spark plug or a loose spark plug wire can cause a rough idle and a loss of horsepower. It can also be caused by a dirty air filter.